1. Field of Invention
This invention relates to hydraulic systems and more particularly to a hydraulic system manifold and a volumetric compensator.
2. Description of Related Art
Hydraulic linear actuators are well known and widely used in industry. In contrast to electromechanical actuators, they are more practical and reliable in applications requiring a large, controllable force. A double-acting hydraulic linear actuator applies such force both in extension and in retraction.
Conventionally, a hydraulic linear actuator is connected to a remote supply of pressurized hydraulic fluid through a closed network of pipes and control valves. However, those are applications where it is desirable for a hydraulic linear actuator to be freestanding and mobile, having a prime mover, a pump, and a closed hydraulic fluid control system all integrated with and located proximate to the linear actuator. Such freestanding actuators are particularly suitable for vehicular applications, such as on automobiles and aircraft.
Prior art freestanding hydraulic actuators are disclosed in U.S. Pat. No. 2,640,323 and 2,640,426 to Stewart B. McLeod and U.S. Pat. No. 5,144,801 to Dino Scanderbeg et al.
It appears that the devices disclosed in each of these references use a reservoir to supply a pump with hydraulic fluid and, where unbalanced cylinders (single rod cylinders) are used, the reservoir absorbs excess hydraulic fluid ejected from the cylinder during rod retraction. Disadvantageously, fluid in a reservoir flows in response to gravitational force, and thus the orientation of the reservoir and the actuator at large may be constrained. If a reservoir-type actuator is improperly oriented, the pump may not be properly supplied with fluid and cavitation may result. Furthermore, generally, a reservoir-type actuator requires more hydraulic fluid to reduce the risk of cavitation.
Conventional freestanding hydraulic linear actuators do not provide for load locking, except through operation of the prime mover. Locking the actuator in position to support a load requires that sufficient fluid pressure be maintained in the actuator cylinder to support the rod. Convention al freestanding hydraulic linear actuators do not normally have the necessary valve configuration to accomplish this task, and thus depend on the prime mover to maintain fluid pressure for load locking.
Thus, there is a need for a way to provide a reservoir-less, freestanding, hydraulic linear actuator that can be operated in any orientation, independent of gravitational forces and which provides for load locking without the operation of a prime mover.